<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <!-- 适配手机 -->
    <meta name="viewport">
    <title>Title</title>
</head>
<body>
    <div style="background-color: red; width: 50px;">
        <div>123</div>
        <div></div>
        <div></div>
    </div>

</body>
</html>